In recent years, an EBG structure has attracted attention as a device or a material. The EBG structure is a structure in which unit structures, which can be expressed by a certain equivalent circuit, are cyclically coupled to each other. The EBG structure has been known to have two main functions.
One of those functions is to provide a high surface impedance in a frequency band including a resonance frequency of an LC parallel resonant circuit that is an equivalent circuit into which the structure is simplified when the structure is viewed in a direction perpendicular to a principal plane of the structure. For example, this mechanism and examples of an EBG structure are disclosed by U.S. Pat. No. 6,538,621 (Patent Document 1).
Another characteristic of the EBG structure is to block transmission of signals or noises in a predetermined frequency band when the structure is viewed in a direction parallel to the principal plane of the EBG structure. In brief, this function utilizes a mechanism in which incoming signals and noises are damped by cyclically arranged unit structures which form an evanescent field with respect to a certain frequency. For example, some proposals with regard to this function are disclosed by United States Patent Publication No. 2006/005001OA1 (Patent Document 2).
Furthermore, there has been proposed a left-handed material that needs no vias and has scalability over restrictions from the via density (see, e.g., Japanese Patent Publication No. 2006-245984 (Patent Document 3)).